one 4-speed down, one to go - PeachParts Mercedes-Benz Forum

bricktron · #1 10-22-2014, 08:03 PM

it's true, my iron transmission had a hole knocked in the case - and the damage was coming from inside the housing! seriously, it went south. i'll have photos when i get the unit home - i decided to eat the bill for a knowledgable shop handling the replacement. it would be challenging for me to tackle alone at home. maybe with help. anyway, i happened to have a spare 4-speed slopeback from a later 240D at home which i'd picked up for $50 alongside a parts car. brought that to the shop and several of us looked at the two of them side by side. the below aren't mine but they are similar.

i was aware of the speedo cable pin changing shape over time, but it did surprise me to find that the shift levers are in different positions- they point opposite directions. i guess i can either (a) fab new rods, (b) find a set of the rods from a later car, or (c) find another early transmission. what do you all think?

bricktron · #2 10-23-2014, 12:41 AM

i should add: anyone with a set of the rods to sell me from a late 240D, please say so!

Frank Reiner · #3 10-23-2014, 01:01 AM

The trans you are considering is a Getrag; there is a slope back version of the iron case trans that is usually referred to as a "slope back".

Look at the front face of both transmissions side-by-side; does the Getrag have the peripheral centering ring of the original? Or just the two dowel pins. The original intermediate plate that is still on the engine may not have provision for the Getrag dowels, and if the Getrag does not have a centering ring there is no way to insure alignment of the input shaft with the crankshaft and clutch.

Stretch · #4 10-23-2014, 01:16 AM

Re: rods

Last time I checked (for someone else) the rods were still available at the dealer. If you get the part numbers sometimes ebay comes up trumps too...

bricktron · #5 10-23-2014, 02:05 PM

good points both. i wrote to tom hanson about the rods, and i will ask my mechanic to check with regard to the centering ring. thanks!

bricktron · #6 10-23-2014, 03:03 PM

OK, tom cited $59 a piece - terrifically expensive for steel rods, but it could be worse - does this mean the three are identical?

VT220D · #7 10-23-2014, 04:41 PM

The shift rods aren't identical and they are specific to the Getrag in the W123 240D. You'll also need the Getrag shifter. The bulk of the shifter assembly is the same but the shift arms are different.

The real show stopper is the intermediate plate mentioned by Mr. Reiner. You will need to replace that plate. The Getrag requires dowel holes for alignment. The later intermediate plate will accommodate the Getrag and the iron box but your early plate will only work with the iron box. I have a 1977 240D intermediate plate on the shelf and it will not work with the Getrag. I found out all about this when I put a Getrag 5 speed behind a 74 OM616.

To change that plate you have to remove the flywheel and you may need to replace the 12 expensive torque to yield bolts holding it on. These bolts can be reused if they meet specs given in the service manual. The flywheel must be marked relative to the crank when removed. There is also a factory centering procedure for the replacement plate.

Getrags use a different clutch slave and clutch line routing.

If I was in your shoes I'd source another iron 4 speed. You can find the slope back iron 4 in 74-80 240Ds. The notch back iron 4 will also fit and was used in 68-73 W115/114 cars. You'll spend much more time and money trying to fit the Getrag to your early car. Exploding iron 4 speeds are far from the norm. Many consider them better than the Getrag.

winmutt · #8 10-23-2014, 05:16 PM

I have shift rods....$60 shipped not sure if they are the ones you need tho.

mike-81-240d · #9 10-23-2014, 06:40 PM

What year did the intermediate plate change?

VT220D · #10 10-23-2014, 10:13 PM

Quote:

Originally Posted by mike-81-240d

What year did the intermediate plate change?

I believe 80 is the first year for the new plate. I have 4 1980 W123s here and all of them have dowel holes. Two of them are 240Ds with iron 4 speeds. By 1981 all the 4 speeds I've seen are Getrag. I suspect the plate was changed in advance of the transmission change.

I looked up the plate on EPC and found the new part simply supersedes the old one. There is no VIN split for the plate. The transition to the new plate has to occur before the introduction of the Getrag or a VIN split would be required and it would match the introduction of the Getrag.

There is a VIN split for the Getrag and it starts at 219675. I looked at one of my 80 240Ds and the VIN is 204xxx yet it clearly has the new plate.

I suppose the new plate may go back to 79 but I haven't seen it. I know the 77 and 78 cars I've parted didn't have one. I think pinpointing the exact timing for the introduction of the new plate will come down to anecdotal evidence but it arrives at least a year before the Getrag.

bricktron · #11 10-29-2014, 01:24 PM

shop is now on the lookout for an iron 4-speed (any tips, let me know). thanks VT220D for all the details. i will now try to unload this getrag as well.

VT220D · #12 10-29-2014, 10:49 PM

Quote:

Originally Posted by bricktron

shop is now on the lookout for an iron 4-speed (any tips, let me know).

There is one thing I can think of that you should watch out for the Iron 4 speed. The cover has a detent assembly for the shift arms. This detent serves both as a shift detent and a lockout to prevent accidental engagement of two gears at once. (See item 14 in the attached EPC picture.)

If the detent is bad the shift arms will not click into place and there will be noticeable free play in the arms. As an example when this part is working each arm will snap into place and when a shift arm is engaged the others will be locked out. A broken detent isn't a deal breaker but it will need to be replaced. If the detent fails it's possible to jam the transmission when the shift rods are disconnected. In the car the shifter and shift rods will keep two gears from being engaged at once but it will feel sloppy. You can always use your old detent - provided it isn't where the hole is!

On any Mercedes transmission the following items apply:

It's a good idea to make sure the output flange is tight. They have been known to loosen. If the donor transmission sat for a while and is rusty output flange rust can ruin the rear seal. I've towed these cars for just a few miles, stood the transmissions on end and watched fluid pour out. Easy fix though.

Shift arm seals and input shaft seals are easy to do when the transmission is out but in my experience they aren't often needed.

Nearly all salvage yards will cut the speedometer cable leaving you to fight with the rusted pinch bolt. It will take some care and skill to remove it. This may not apply to you but I'm in one of the rustiest parts of the universe!

Any transmission that has sat outside is best avoided. Here they get buried in snow above the vent and when the show melts water ends up inside. I've had two like that. Input shaft turns a half turn and stops when the rusty side of the gears start to mesh. A good transmission will feel smooth and even in every gear. You will be able to feel the gears but it shouldn't feel notchy or vary in effort through a complete revolution of the output shaft. Some input shaft play is normal but excessive play indicates a bad input shaft bearing. This is more of a Getrag issue.

If you drain the transmission and it's full of gear oil - run. The sulfur in gear oil will attack brass synchros. I had one that wasn't even yard drivable because it popped out of first and this was the reason.

I'd try to find one from a nearby forum member or from complete car in a salvage yard. If you can check out the car you can see when it was last on the road and you can usually figure out what killed it. Indicated mileage won't tell you anything. On the W123 the odometer is nearly useless because it probably doesn't work and on the W115 it's useless even if it does.

Other than that I recommend new shifter bushings on both ends and a cleaning/relube of the shifter. The shift rods will require adjustment per the manual and the procedure is easy. Of course you should change the fluid and check/replace the transmission mount and flex discs. Before installing the transmission be sure to check that the fill/drain plugs can be removed. Any clutch/driveshaft related items are best done now.

Dan Stokes · #13 10-30-2014, 09:05 AM

Great info from VT220D!

Let me add that my 240D (that I got my 4 speed from) was sold cheap because it badly needed a slave cylinder. I would ALWAYS change the slave when you're down there - seems to be a pretty common issue.

But buying a trans from a running car is a great deal - best chance of knowing what you're getting. Mine was smooth and solid from the get-go. Someday I'll get the truck running and find out if the trans actually works!

Dan

bricktron · #14 10-31-2014, 01:17 PM

all great info, i had no idea about that detent assembly. say no to rusty transmissions! my slave cylinder was actually already changed recently. thanks folks.

Frank Reiner · #15 10-31-2014, 11:54 PM

Brickman:

Have you checked this out from benzguy300? It's an iron 4-speed.

"Very rare manual transmission kit for W126" In the Parts section